Apparatus for forming metal tubes to the shape of a frustum of a pyramid



United States Patent O 3,354,682 APPARATUS FOR FORMING METAL TUBES TO THE SHAPE F A FRUSTUM 0F A PYRAMID Antoine Dupuy, Rue Peyrard, Saint-Bonnet-le-Chateau, Loire, France Filed Apr. 14, 1965, Ser. No. 448,053 Claims priority, application France, Apr. 17, 1964, 8,921, Patent 1,401,473 2 Claims. (Cl. 72-192) ABSTRACT OF THE DISCLOSURE Apparatus for producing tubular frustums of a pyramid from a tubular blank in which two spaced rolls are each provided on its periphery with an engraving of a gradually decreasing depth and breadth, the cross-sections of said engravings in transverse section cooperatively defining the outer surface of the frustum to be obtained. A polygonal frustopyramidal mandrel is provided having a shape matching the inner surface of the frustum to be obtained, the mandrel -being adapted to carry the tubular blank and be urged therewith through the gap between the rolls in a direction perpendicular to the plane of the axes of the rolls, to cause the blanks to engage the engravings of the rolls. The input and output ends of each engraving is separated by a relieved portion of the corresponding roll.

It is known to transform a cylindrical or frustoconical tube into a tubular frustum of a pyramid having for instance four sides, that is having a square transverse crosssection, by either a shrinking machine in which the tube is simultaneously struck at several points or by a press.

The quality of the tubes having the shape of a frustum of a pyramid obtained in accordance with such prior methods is poor, chiefly as regards the lack of flatness of their surfaces. On the other hand, the execution of such prior methods is somewhat long and is suitable only for tubes of a comparatively small cross-section.

The present invention has as an object a novel method which is much more economical because it is speedier and because it allows obtaining tubes the shape of which is perfect While their mechanical resistance is substantially increased.

The invention consists chiefly in fitting the tubular blank, whether cylindrical or conical over a mandrel of which the outer shape of which matches that to be assumed by the inner surface of the tube when finished, after which the blank fitted on its mandrel, is caused to enter a rolling gear, preferably of the returning roll type, of which the rolls operate during a fraction of a revo1ution and return to their starting point during the idle period corresponding to the end of the operative revolution, said rolls having engravings of a gradually decreasing depth and breadth, matching the outer frustopyramidal shape to be given to the tube.

The above-mentioned pyramidal shape is given preferably to the blank by a succession of operative steps between the rolls of several pairs of rolls.

The gap between two rolls allows introducing between them the blank fitted on its mandrel, whereas the rotary movement of said cylinders ensuring the rol-ling procedure returns the tube forwardly during its deformation, that is, it urges the tube towards the operator whereby the tube is released at the end of its travel.

The improved method according to the invention thus enables the inner and outer cross-sections of the tubular frusto-pyramid to be very accurately obtained. It is consequently possible to define the thicknesses of the tube at different points and in particular to remove the eXtraice thicknesses in those parts where they may occur detrimentally, that is over the fiat sections of the frustum, as a consequence of the reductions in cross-section and consequently it is possible to produce an elongation of the tube through extrusion of the metal, which may lead to a substantial increase in length, of a magnitude of 10%.

On the other hand and according to a more particularly advantageous method, the ridges of the mandrel are rounded and the connections between the successive flat surfaces of the engravings of the cylinders are flattened so that it is possible not only to reinforce the ridges of the finished work which forms its weakest parts, but it also allows giving the outer outline of the work a bevelled shape.

Obviously, the shape of a frustum of a pyramid may be given to the blank throughout its entire length or only over a fraction of the latter.

The present invention 4will be readily understood from the reading of the following description, reference being made to the accompanying diagrammatic drawings illustrating by way of example the manner of obtaining a tubular frustum of a pyramid having a square outline. In said drawings:

FIGS. l and 2 are transverse cross-sections of the arrangement used for the execution of the invention, respectively before land during the rolling operation.

FIG. 3 is a cross-section on a larger scale through line 3-3 of a part of FIG. 2,

FIG. 4 illustrates on the same scale as FIG. 3, a crosssection of the finished tubular frustum of a pyramid,

FIG. 5 shows on a still larger scale, one of the ridges of the finished tubular frustum of a pyramid with further detail.

In FIGS. l to 3, 1 and 2 designate the two rolls of a pair of rolls provided each With a recess or engraving 3, the rbottom of which is eccentric with reference to the roll.

Said cylinders revolve in opposite directions as illustrated by the arrows x and y and they are each provided with a relieved section 4.

The blank tube is designated by 5 and the mandrel by 6.

The engravings 3 in the rolls 1 and 2 have the transverse outline illustrated in FIG. 3. Therein it is seen that each engraving is bounded by two surfaces 7 sloping at with reference to each other and at 45 with reference to a plane perpendicular to the axes of the rolls, the ends of each surface which registers with the other surface 7 or with the periphery of the cylinder, being cut off as Shown at 8.

The parts of the engraving in the roll 1 associated with those in the roll 2 define between them an empty space having a square cross-section the corners of which are cut ofi and the depth of which decreases from the input up to the output point 10.

The mandrel 6 is in the shape of a solid square frustum of izpyramid, the ridges of which are rounded as shown at When the end of the mandrel engages the stop 11 (FIGS. 1 and 2) defining the starting point of its path, said stop acts on an electric switch, a pneumatic valve or the like releasing means starting the rotation of the rolls.

The blank is thus carried along W-ith its mandrel in the direction of the arrow p, that is towards the operator (FIG. 2) and the blank is thus shaped by rolling as provided by its matching intimately the ou-ter surface of the mandrel 6.

When, upon rotation of the rolls, the narrower ends 10 of the engravings in the rolls 1 and 2 face each other, the operation is at an end and the operator removes -the blank and the mandrel so that he may subject Ithe work to one or more further finishing operative steps if required.

FIG. 5 shows in cross-section a fraction of the square tube obtained. It is found that the thickness e of the fiat sections of said square is constant Iand is retained throughout the length of the tube in spite of the shrinking o-f its cross-section. Said thickness e may be even still further reduced if required. During yits shaping, the length of the tube increases, which leads to a saving of metal. In contradis'tinction, the thicknesses a, b, c Iat diierent points of the corner ridges are larger than the thickness e by reason of the large radius 15 (FIG. 4) 'assumed by the blank under the -action of the Irounded ridges of the mandrel.

Such a reinforcement of the ridges yof the tubular frustum of a pyramid is obtained, even in the case of a bevel 13 being formed at 45 with reference to the side walls of the work on the outside of lthe latter, as provided by the corresponding at cut off terminal sections of the engravings 3; this gives the work la clean, aesthetic and rectilinear appearance, which can-not `be obtained with the conventional methods.

In the case illustrated, it has been yassumed that the tube to be obtained should include a frustum of a pyramid provided with an extension 14 retaining the original cylindrical shape of the blank.

Through the method disclosed, it -is possible to obtain tubes of any desired cross-section in the shape of a frustum of a pyramid, intended more particularly but not exclusively to serve -in the execution of -the legs of seats, tables and the like.

Obviously and as apparent from the preceding disclosu-re, the present invention is by no means limited to the embodiment disclosed hereinabove solely by way of example and it covers in contradistinction all the modications thereof falling within the scope of the accompanying claims.

What -is claimed is:

1. In an arrangement for producing tubular frustums of a pyramid out of va tubular blank, the provision of two rolls separated by a gap and provided each Ialong its periphery with an engraving of a gradually decreasing depth and breadth and the cross-section of which roll engravings, when facing each other on either side of the gap between the rolls, cooperatively decline the outer surface of the frustum to be obtained and the polygonal frustopyram-idal mandrel Shaving a shape which matches the inner surface of the lf-rustum to be obtained, said mandrel being adapted to carry the tubular blank land to be urged therewith through the gap between the rolls in a direction perpendicular to the plane of the axes of the rolls, to m-ake the blank engage the engravings of the rolls, the input and output ends of each engraving being separated by a relieved portion of the corresponding roll.

2. In an arrangement for producing tubular frustums of a pyramid out of a tubular blank, the provision of two rolls separated by a gap and provided e-ach along its periphery with an engraving of a gradually decreasing depth and breadth `and the cross-sections 'of which roll engrav ings, when facing each other on either side of the gap between the rolls, form a regular polygon the corners of which are cut olf, said polygon corresponding to the outer surface of the frustum to be obtained, and a polygonal frustopyramidal mandrel having bevelled ridges and a shape which matches the inner surface of the frustum to be obtained, said mandrel being adapted to carry the tubular blank and to be urged therewith through the gap between the rolls in a direction perpendicular to the plane of the axes of the rolls, to make the blank engage the engravings of the rolls, the input and outputends of each engraving being separated by a relieved portion of the corresponding roll.

References Cited UNITED STATES PATENTS Re. 19,734 10/1935 Heddon 72-198 274,964 4/ 1883 Ostrander 72-209 480,609 8/ 1892 Neve-gold 72--199 738,067 9/1903 Reimann 72-193 1,007,924 11/1911 Curr 72--199 1,510,586 10/1924 Davis 72--209 1,810,885 6/1931 Neuberth 72-208 2,085,963 7/1937 Ferm et al. 72-198 2,347,904 5/1944 Greulich 72-366 CHARLES W. LANHAM, Primary Examiner.

A. RUDERMAN, Assistant Examiner. 

1. IN AN ARRANGEMENT FOR PRODUCING TUBULAR FRUSTUMS OF A PYRAMID OUT OF A TUBULAR BLANK, THE PROVISION OF TWO ROLLS SEPARATED BY A GAP AND PROVIDED EACH ALONG ITS PERIPHERY WITH AN ENGRAVING OF A GRADUALLY DECREASING DEPTH AND BREADTH AND THE CROSS-SECTION OF WHICH ROLL ENGRAVING, WHEN FACING EACH OTHER ON EITHER SIDE OF THE GAP BETWEEN THE ROLLS, COOPERATIVELY DEFINE THE OUTER SURFACE OF THE FRUSTUM TO BE OBTAINED AND THE POLYGONAL FRUSTOPYRAMIDAL MANDREL HAVING A SHAPE WHICH MATCHES THE INNER SURFACE OF THE FRUSTUM TO BE OBTAINED, SAID MANDREL BEING ADAPTED TO CARRY THE TUBULAR BLANK AND TO BE URGED THEREWITH THROUGH THE GAP BETWEEN THE ROLLS IN A DIRECTION PERPENDICULAR TO THE PLANE OF THE AXES OF THE ROLLS, TO 